1. Field of the Invention
The invention relates to a control apparatus for a variable operation angle mechanism that varies the operation angle of an intake valve. More particularly, the invention relates to an improvement of a control structure when an engine is stopped that improves high temperature startability.
2. Description of the Related Art
Variable operation angle mechanisms that vary the operation angle of intake and exhaust valves are being used as mechanisms applied to engines in vehicles and the like. In many engines provided with such a variable operation angle mechanism, when the engine is stopped, the operation angle of the intake valve is set to an optimum operation angle to ensure startability the next time the engine is started. Japanese Patent Application Publication No. 2005-299594 (JP-A-2005-299594), for example, proposes technology that reduces the drive torque of a starter used for starting, thereby improving the startability of the engine, by increasing the operation angle of the intake valve and reducing the compression ratio in the cylinders when the engine is stopped.
Incidentally, in recent years, efforts have been made to increase the compression ratio of an engine in order improve fuel efficiency and the like. However, an engine with a high compression ratio is susceptible to knocking when the engine is restarted at a high temperature (hereinafter also referred to as a “high temperature restart”). Such knocking during a high temperature restart can be avoided by increasing the operation angle of the intake valve and reducing the compression ratio in the cylinders when the engine is stopped. Therefore, in the related art described above, knocking during a high temperature restart can be avoided by increasing the operation angle of the intake valve to the point at which knocking during a high temperature restart can be avoided, when the engine is stopped. However, if the operation angle of the intake valve is increased to the point at which knocking dining a high temperature restart can be avoided, the compression ratio may be too low for a normal start that is not a high temperature restart, and as a result, it may no longer be possible to ensure sufficient startability during a normal start.